能否使用wp_get_nav_menu_items输出WordPress三级菜单项？

Absolutely, the wp_get_nav_menu_items() function does retrieve third-level (and even deeper) menu items—this isn't a limitation of the core WordPress function itself. The issue you're hitting is almost certainly how the mega-menu script you're adapting is processing and structuring the returned items.

Why most examples only show two levels #

A lot of basic menu scripts stop at two levels because they only handle direct parent-child relationships (top-level items → their immediate children) without adding logic to recursively check for deeper nested items. The script you're using might be filtering the menu items to only include top-level and second-level entries, or it's not building out a hierarchical structure that accounts for third-level items.

How to fix this #

First, double-check that your menu in the WordPress admin actually has third-level items set up correctly (i.e., you've dragged menu items under second-level items to nest them). Once you confirm that, you'll need to adjust the script's menu processing logic to handle deeper hierarchies.

Here's a simple recursive function you can use to restructure the flat array returned by wp_get_nav_menu_items() into a nested hierarchy that includes all levels:

function build_nested_menu($menu_items, $parent_id = 0) {
    $nested_menu = array();
    
    foreach ($menu_items as $item) {
        // Check if this item is a child of the current parent
        if ((int)$item->menu_item_parent === $parent_id) {
            // Recursively find children of this item
            $child_items = build_nested_menu($menu_items, $item->ID);
            
            // Add children to the item if there are any
            if (!empty($child_items)) {
                $item->children = $child_items;
            }
            
            $nested_menu[] = $item;
        }
    }
    
    return $nested_menu;
}

// Usage with your menu:
$menu_slug = 'your-menu-slug'; // Replace with your menu's slug/name/ID
$flat_menu_items = wp_get_nav_menu_items($menu_slug);
$hierarchical_menu = build_nested_menu($flat_menu_items);

Then, in your mega-menu template code, you'll need to loop through the hierarchical structure recursively. For example:

function render_mega_menu($menu_items) {
    echo '<ul>';
    foreach ($menu_items as $item) {
        echo '<li><a href="' . esc_url($item->url) . '">' . esc_html($item->title) . '</a>';
        
        // If this item has children (including third-level), render them
        if (isset($item->children)) {
            render_mega_menu($item->children);
        }
        
        echo '</li>';
    }
    echo '</ul>';
}

// Render the full menu
render_mega_menu($hierarchical_menu);

Things to check if it still doesn't work #

• Make sure no other plugins or theme functions are filtering wp_get_nav_menu_items to exclude deeper items (check for uses of the wp_get_nav_menu_items filter hook).
• Verify that the third-level menu items in your admin have the correct parent ID set (you can debug this by var_dump($flat_menu_items) to see the menu_item_parent values for each item).
• Check if the original mega-menu script has hardcoded limits (e.g., loops that only run twice for top and second levels) that you need to remove or replace with recursive logic.

内容的提问来源于stack exchange，提问作者Connie